Correct Water Change Methodology

I tend to let it sit for just a few minutes. It is my understanding that the de-chlorinators work almost instantly.

I don't see any reason in letting the water sit before you put it in the tank. I fill up the tank with my Python and then add some declorinizer after. I also use the AquaPlus.

The only time you should worry about letting your water sit is if the temperature difference between the new water and the tank is a big one, or if you're not using a dechlorinator. I've never had a problem adding the water direct from the tap and adding dechlor after....

questoin: when adding water from the tap and dechlorinating after it gets added WHILE spawning is taking place, will the chloring have adverse effects on the eggs?

Unlikely. The membrane on fish eggs is pretty solid stuff. It protects the fry from the outside environment. Hatcheries will use a dilute bleach solution to clean wild eggs--they swirl the eggs through it very quickly, then seive them off into clean water. Kills any nasties that might be in the water and avoids bringing that into the isolation station.

Heck, we add formalin drips to the egg incubators for fungus, and that doesn't have any effect on the hatch rates compared to incubators that aren't prone to fungus infections.